The noun entity, as it is known today, first came into use in the English language in 1596 in the Middle English form entitie. The Oxford English Dictionary defines the word as “being, existence, as opposed to non-existence; the existence as distinguished from the qualities or relations, of anything.” In layman's terms it is thing that exists.1 This word traces back to the Latin verb esse, which means to be and also has roots in Ancient Greece.2 The word entity was originally used in philosophy and was considered in an abstract sense; however, it has evolved into the concrete meaning it has today.
In ancient Greece, Aristotle was concerned with that which is and determined that the central question surrounded substance. He is quoted saying “to ti ēn einai,” which means the what it was to be. The noun on in Greek was created from the verb einai – to be, to define something that is. Here Aristotle and other philosophers were concerned with what is now entity (on) in an abstract sense.3
Since there was no noun for what it was to be in Latin, the word on was translated from Greek. This was done by borrowing the structure of the noun from the Greeks, deriving the noun from the Latin verb esse (to be), creating the word ens.4 Ens was also based off the structure of the Latin word absēns, which translates into absent in English today. This was because absēns defined the absence of something and ens would now define the existence of something.2
Ens refers to something with existence and also meant essence, however the later definition is no longer in use.2 This word is often used in law and philosophy. For example, in law, ens legis means a being of the law, described an entity created by the the law with an independent legal system.5 In philosophy ens realissimum, means the most real thing, referring to God.6
The suffix -ity originates from Latin suffixes such as -tās which meant to express a condition. This suffix evolved into -itāt and -itās in classical Latin.7
The word ens was combined with the suffix -itāt, becoming entiāt-em. This word evolved into entity, as it is known today; however it took different forms in Middle English including entitye, eventually becoming entity.1
The word entity is no longer used or considered in an abstract sense, but has a concrete meaning; it is a thing that exists. To say that one thing is an entity means that it exists, whether tangible or intangible.
1 "entity, n.". OED Online. September 2012. Oxford University Press. http://www.oed.com/view/Entry/62904?redirectedFrom=entity (accessed November 18, 2012).
2 "ens, n.". OED Online. September 2012. Oxford University Press. http://www.oed.com/view/Entry/62619?redirectedFrom=ENS (accessed November 18, 2012).
3 "Aristotle." In Oxford Dictionary of the Classical World, Oxford University Press. (, n.d.). Retrieved 18 Nov. 2012, from http://www.oxfordreference.com.proxy.lib.uwaterloo.ca/view/10.1093/acref/9780192801463.001.0001/acref-9780192801463-e-221
4 Speake, Jennifer, inasdf and Mark LaFlaur. "ens." In The Oxford Essential Dictionary of Foreign Terms in English, Oxford University Press. (, n.d.). Retrieved 18 Nov. 2012, from http://www.oxfordreference.com.proxy.lib.uwaterloo.ca/view/10.1093/acref/9780199891573.001.0001/acref-9780199891573-e-2179
5 Fellmeth, Aaron X., inasdf and Maurice Horwitz. "Ens legis." In Guide to Latin in International Law, Oxford University Press. (, n.d.). Retrieved 18 Nov. 2012, from http://www.oxfordreference.com.proxy.lib.uwaterloo.ca/view/10.1093/acref/9780195369380.001.0001/acref-9780195369380-e-607
6 Blackburn, Simon. "ens realissimum." In The Oxford Dictionary of Philosophy, Oxford University Press. (, n.d.). Retrieved 18 Nov. 2012, from http://www.oxfordreference.com.proxy.lib.uwaterloo.ca/view/10.1093/acref/9780199541430.001.0001/acref-9780199541430-e-1086
7 "-ity, suffix". OED Online. September 2012. Oxford University Press. http://www.oed.com/view/Entry/100360?redirectedFrom=-ity (accessed November 18, 2012).